The present invention relates to an antenna apparatus including a feed array and, in particular, to an antenna apparatus that includes a compound curve antenna structure for imaging purposes.
Antenna systems with a reflector or collimating unit are well-known that send a transmit beam and receive a return beam in order to obtain desired information based on the contents of the return beam. A variety of such imaging systems have been devised that rely on a specifically shaped beam collimating unit, such as a parabolic-shaped reflector. Outputs from a feed array are applied to a reflector or other collimating unit to generate the transmit beam having a desired direction. A receive beam or the return beam is received by the collimating unit and applied to the feed array from which useful information can be obtained by suitable processing.
In designing the antenna system, certain key parameters are taken into account including size, the number of components, cost, gain and field of view. Generally, as the number of antenna components increases, the cost of the antenna system becomes greater. The gain of the antenna system is typically improved with a larger collimating assembly, such as a reflector or lens. However, this means a greater size and usually an increased cost. Expanding the field of view or scan range of the antenna system also means a larger feed array of energizing elements which results in a higher cost. Additionally, it is generally desired to have a high instantaneous bandwidth, while avoiding any increase in cost, size or weight of the antenna system.
When designing an antenna system, numerous and complex factors must be considered to arrive at an acceptable transmit/receive antenna system. It would be beneficial, therefore, to provide an antenna system that more advantageously balances these numerous factors whereby a desired or appropriate gain and field of view, for example, are achieved, while optimizing certain parameters such as instantaneous bandwidth and reducing others, such as size, cost and weight. Such an antenna system should be able to generate a transmit beam and process a return beam having useful information to be analyzed, while constituting an optimal design that includes a unique collimating assembly and accompanying feed array.
In accordance with the present invention, an antenna apparatus is provided having a beam control system and a beam collimating system in which the beam collimating system is characterized by having a compound curve antenna structure. The compound curve antenna structure can be two-dimensional or three-dimensional. The beam collimating system can include one, or more than one, compound curve antenna structure(s). The compound curve antenna structure includes at least first and second curved reflector sections. These two curved reflector sections can be located symmetrically about a defined reflector axis. The first curved reflector section is spaced from the second curved reflector section. When the compound curve antenna structure is three-dimensional, these two sections are part of a body of revolution. The two compound curved reflector sections have an aperture end and a base end. In at least the two-dimensional configuration, the feed array of the beam control system is disposed between these two reflector sections and adjacent to their base ends. Preferably, the first and second curved reflector sections are parabolic cylindrical reflectors, although other compound curved reflector sections might be used, such as hyperbolic, elliptical or other multi-curved configurations.
The feed array has a number of feed or energizable elements that, when energized, control generation of a transmit beam and/or control receipt/recovery of a return beam that can be, but need not be, based on the transmit beam. The return beam contains useful information related to an object or location of interest. The information associated with the return beam can be analyzed or processed in order to present or provide it in an intelligible form. The transmit and return beams can be controlled to scan through a range of angles that constitutes the field of view for the antenna apparatus, particularly using the beam collimating system which includes the compound curve antenna structure. With regard to such scanning of these beams, the feed elements of the feed array are selectively activated or energized to cause such beams to move in one or both of azimuth and elevation. Significant to the present invention, such control of the energization of the feed elements for an antenna apparatus having a particular compound curve antenna structure is based on predetermined data or other information stored in memory storage of the beam control system. In the two-dimensional compound curve reflector structure embodiment, the predetermined data relates to identification of reflections, and information related thereto, on the first and second curved reflector sections, together with reflections that strike feed array elements directly without first contacting the first and second curved reflector sections. By way of example, depending on the particular scan angle of the range of scan angles associated with the particular compound curve antenna structure, the receive or return beam may reflect from one or both of the first and second curved reflector sections and then strike one or more of the feed elements of the feed array. On the other hand, there may be no such reflections associated with at least some of the electromagnetic (EM) radiation of a return beam, which EM radiation strikes the one or more feed elements directly. In order to properly and accurately control the processing of a return beam at a desired scan angle, it is necessary to use the predetermined data related to reflections: (1) on portions of the compound curve antenna structure and (2) in direct contact with the feed array, in controlling which feed elements should be energized for a particular scan angle. More specifically, for a particular configured compound curve antenna structure in communication with an appropriate feed array (e.g., reference feed array), a reference beam, which emulates a return beam, can be directed to the compound curve antenna structure at a known scan angle. The reflections or striking/contacting of rays of the reference beam are observed in connection with identifying the specific feed elements that receive such rays. Based on such observations, the predetermined data associated with that particular scan angle is found and can be stored. Then, when that particular compound curve antenna structure, or one that is equivalent thereto, is utilized, the identified feed elements can be energized in accordance with the predetermined data that was stored based on use of the reference beam and the reference feed array.
In conducting the analysis related to a reference beam for a particular three-dimensional compound curve antenna structure, contributions of successive reflections on the structure are determined related to the total power collected by the feed elements of the feed array. In one embodiment, the feed distribution is considered to be converged or finished when the power delivered by the final reflection falls below a predetermined percent (e.g. 1%) of the total power collected from all collections. With regard to conducting the analyses for a number of reference beams at different scan angles for a particular compound curve antenna structure, a device (e.g., including software) can be employed that monitors the simulated, for example, EM radiation (electromagnetic (EM) fields or RF signals) of the reference beam in conjunction with any of its reflections. In particular, where such EM radiation contacts reflector portions and which feed elements are contacted by EM radiation are monitored.
With respect to the properties and/or operation of the antenna apparatus, certain key aspects are noted when utilizing the compound curve antenna structure. For a particular scan angle during scanning, as the scan angle increases towards a maximum angle of scan, which constitutes the outer edge of the field of view, the number of feed elements that are energized to control the antenna beam becomes less. When the compound curve antenna structure is two-dimensional, it has two focii. The two focii are located at the base ends of the two curved reflector sections. At the maximum angle of scan of the antenna beam, substantially all feed elements that are energized are located adjacent to both an end of the feed array and an end of one of the first and second curved reflector sections. Relatedly, as the angle of scan associated with the antenna beam moves away from the maximum angle of scan, the greater the number of feed elements that are energized to provide the antenna beam.
When the compound parabolic antenna structure is three-dimensional, the return beam can have a single linear polarization resulting from a dual-polarized feed provided during generation of the transmit beam on which the return beam is based. Relatedly, the feed array independently controls two orthogonal polarizations in communicating with the three-dimensional compound curve antenna structure. In one preferred embodiment, there are a number of three-dimensional compound curve antenna structures that are arranged in an array. By using this configuration, a higher bandwidth, particularly a higher instantaneous bandwidth, is provided whereby relatively more information is obtainable in a relatively less period of time.
Based on the foregoing summary, a number of salient features of the present invention are recognized. An antenna apparatus can be provided that reduces the size, weight and cost of a control/processing system including a feed array for a desired or given gain and field of view associated with a particular beam collimating system that includes a compound curve antenna structure. Relatedly, the scan range or field of view that can be achieved is greater than that for non-compound curve antenna structures, such as one-dimensional reflectors or lenses that can be used with sizes of feed arrays comparable to that utilized in the present invention. Importantly, the present invention requires a two-dimensional or three-dimensional antenna structure in combination with a feed array disposed at a predetermined position relative to this structure. As a result, a relatively higher gain with a relatively increased field of view can be obtained while reducing the cost, weight and size thereof over antenna designs that do not have a compound curve antenna structure.
Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings.